Telephone



(NOMOM') T. A. EDISON.

. TELEPHONE. I No. 406,567. Patented July 9., 1889..

N- PETERS. Phnlo'uthngrapher. Wmhingluu. D C.

UNITED STATES PATENT OFFICE.

THOMAS A. EDISON, OF MENLO PARK, NEW JERSEY.

TELEPHONE.

SPECIFICATION forming part of Letters Patent No. 406,567, dated July 9,1889.

Application filed February 19, 1886. Serial No. 192,485. (No model.)

To all whom it may concern.-

Be it known thatI, THOMAS A. EDISON, of Menlo Park, in the county ofMiddlesex and State of New Jersey, have invented a new and usefulImprovement in Telephones, (Case No. 661,) of which the following is aspecification.

My invention relates to that class of telephones wherein a body ofcarbon-granules is held between metal surfaces, one of which isconnected with the diaphragm of the instrument and acts upon the carbonto vary the resistance of the circuit in unison with the sound-waves.The object I have in View is to produce for this purpose a form ofcarbon which will be free from the objections incident to the use of thecarbon heretofore employed, in that it will not blacken themetalsurfaces in contact with it, and will not by use become finely powderedand liable to pack. The result is a more durable instrument and onewhich maintains its adjustment better and is capable of being used inany position.

My improved carbon is made by the carbonization of anthracite or hardcannel coal by subjecting it to a high heat in a manner similar to thecarbonization of materials for the conductors of incandescent electriclights. It is then powdered into granules which will pass through atwenty or thirty mesh screen, and is ready for use as the electrode of atelephone.

In the accompanying drawings the figure represents parts of a well-knownformof telephone with an electrode of my peculiar carbon.

A is the diaphragm, and B a part of the case. 0 is the electrode ofcarbon-granules, produced, as before explained, from hard coal, and heldin a metalcup D, carried by an adj usting-screw E. A metal plate F,carried by the diaphragm, presses on the carbon in the cup. The cireuitconnections 1 2- are such that the current passes through the carbonelectrode.

What I claim is 1. An electrode for telephones composed of a body ofgranules of carbonized hard coal, substantially as set forth.

2. In a telephone, the combination, with a diaphragm, of an electrodecomposed of a body of granules of carbonized hard coal i11- cluded inthe circuit and acted upon by the diaphragm to vary the resistance ofthe circuit, substantially as set forth.

3. In a telephone, the combination, with a diaphragm, of an electrodecomposed of a body of granules of carbonized hard coal, and metalsurfaces between which such body of carbon-granules is held, one of suchmetal surfaces being controlled by the diaphragm,

A. W. KIDDLE, E. O. ROWLAND,

